This invention relates to an elevator speed control system, and more particularly to a speed control system for automatically controlling a speed of an elevator car by comparing a command speed signal with a negatively fed-back signal for the actual speed of the elevator car.
Conventional speed control systems of the type referred to have comprised an electric generator for energizing an electric motor for driving an elevator car, the command speed generator for generating a command speed signal, a speed sensor for sensing the actual speed of the elevator car, and a field control circuit for comparing the command speed signal with the actual speed signal negatively fed back from the speed sensor to automatically control the speed of the elevator car in accordance with the result of the comparison.
In the case of high rise elevators, a mechanical system formed of the elevator car and associated mechanical components has had such a low resonance frequency that the mechanical system may interfere with the speed control system resulting in the possibility of causing oscillation. In order to avoid this objection, the speed control system may have a decreased response which is not desirable. Also it is difficult to increase the resonance frequency of the mechanical system for the same purpose.
Accordingly it is an object of the present invention to provide a new and improved elevator speed control system which is prevented from becoming unstable even if an associated mechanical system has a decreased resonance frequency thereby to ensure the stable operation of an elevator car involved.